1. Technical Field
This invention relates to a method of manufacturing succinic acid and ammonium succinate solutions using fermentation.
2. Background Art
Succinic acid and its derivatives are widely used as raw materials in the manufacture of foods, perfumes, cosmetics, and medicines. Furthermore, succinic acid has been recently used in monomers of biodegradable plastics. The succinic acid used in these applications is produced by a petrochemical method. Alternatively, the production of succinic acid by fermentation has been recently investigated using carbohydrates of plant origin as raw materials.
When producing succinic acid by a fermentation method, the culture pH should generally be maintained at around neutral, so that microorganisms can exhibit the necessary and sufficient activities. As a neutralizing agent, calcium hydroxide, sodium hydroxide, magnesium hydroxide, ammonia, calcium carbonate, sodium carbonate, magnesium carbonate and ammonium carbonate, etc. can be used. As a result, the corresponding succinic acid salts can accumulate in the culture solution.
Among the succinic acid salts, it is known that calcium succinate has a low solubility, and can precipitate as crystals into the culture solution (JP62-294090A). Usually, the culture solution contains a mixture of raw materials for fermentation, such as sugars, various additives, such as nutrients for the chosen microorganism, and by-products produced by the metabolism of microorganism, etc. Because calcium succinate is easily removed from the culture solution due to precipitation of the crystals, purification of succinic acid can be simple. Furthermore, since further purification methods to isolate the succinate crystals, such as concentration, are unnecessary, the precipitation of calcium salt is advantageous from the viewpoint of energy consumption.
A typical method of separating succinic acid from succinate salts is to lower the pH until free succinic acid is generated by adding an acid, such as sulfuric acid. For calcium succinate, a method of obtaining succinic acid by using sulfuric acid is known (JP3-30685A). However, this method has limitations since sufficient amounts of calcium sulfate do not precipitate as a by-product.
To separate succinic acid from succinates without using acid, electrodialysis has been proposed (JP2-283289A). Since bases which separate from succinic acid during the purification process are reused as neutralizing agents in fermentation, by-products are not produced. However, this method is limited to the succinic acid salts with monovalent bases, such as sodium succinate and ammonium succinate. For calcium salt, this method is unsuitable due to the precipitation and build-up of debris on the membrane used for filtration. For these reasons, studies using calcium compounds as neutralizing agents have not been conducted in recent years.
Alternatively, when succinic acid is obtained from ammonium succinate using sulfuric acid, ammonium sulfate is produced as a by-product. A method of preventing the generation by-product salts was finally proposed by pyrolyzing the produced by-product ammonium sulfate at 300° to produce ammonium hydrogen sulfate and ammonia, and then reusing them in the process (JP2001-514900A).
In addition, a method of using acetic acid has also been proposed for obtaining succinic acid from ammonium succinate (JP2004-196768A). Generation of by-product salts is prevented by pyrolyzing the ammonium sulfate produced as a by-product, resulting in production of acetic acid and ammonia, and then reusing them in the process. As mentioned above, ammonium succinate can be used as a starting material in the purification process of succinic acid.
Ammonium succinate can accumulate in the culture solution by using ammonia, or the like, as a neutralizing agent in the fermentation process. However, it is known that ammonia is not the most efficient neutralizing agent for producing succinic acid, and from the viewpoint of productivity and yield during fermentation, magnesium compounds can be effective (WO2005/026349A).
Various purification methods are applicable to the magnesium salt, which results in a favorable form of this salt during the fermentation process. Furthermore, and in view of the methods disclosed in JP2001-514900A and JP2004-196768A which do not generate salt by-products, a method in which the salt is substituted was proposed to convert the ammonium salt into a more favorable form (JP2005-295998A). The magnesium compound produced by substituting the salt is reused as a neutralizing agent in the fermentation process. Magnesium succinate which is produced in the fermentation process is dissolved in the culture solution, and usually does not precipitate as crystals. Therefore, the salt substitution step is carried out by adding ammonium carbonate or the like to the culture solution. As a result, the mixture in the culture solution, other than magnesium succinate, is carried into the ammonium succinate solution which is the starting material for the purification process. Therefore, an additional step is necessary to remove the complicated mixture before or after the salt substitution step.
An efficient method of manufacturing ammonium succinate solution by fermentation has not been previously described.